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Comment by xenadu02 | Hacker News Reader

I assume the JIT isn't optimizing until the functions execute a certain number of times. Given the speed difference maybe it isn't even natively compiling at first and using the interpreter.

I don't know about Java but in .NET there's a call you can make to force the dynamically generated lamba expression to be compiled immediately.

Of course if you're being really adventurous you can use IL emit to build a function up from IL opcodes.

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Yes. The author didn't note his testing methodology. JMH (Java Microbenchmark Harness) is the gold standard for executing Java benchmarking tests:

http://openjdk.java.net/projects/code-tools/jmh/

It takes care of details like JVM warm-ups. ensuring sufficient invocations for JIT compilation to have occurred, etc.

Although sometimes the performance when interpreted before warm-up is important.

Testing with CompilerControl.Mode.EXCLUDE in JMH is still more reliable than testing manually, when you don't know if it got compiled or not.

Interpreted code is a case where method handles should be much faster than the generated accessor classes used by reflection - lambdas and method references are faster than an inner class implementing a functional interface before jit compilation. Afterwards, performance tends to be sameish.

That's the kind of solution I've used before when performing reflection in a tight loop. The important thing there is to cache the result of the compiled expression or the dynamic IL code because the compile time/emit is slower than a single use of reflection.

> The important thing there is to cache the result of the compiled expression or the dynamic IL code because the compile time/emit is slower than a single use of reflection

I came across some code a few weeks ago that skipped this step. It wasn't called remotely often enough to justify the complication in the first place (low volume internal web app) but it didn't cache the result so it ended up making things slower. Thanks to the wonders of RenderAction in MVC it compiled the dynamic IL 20 times per page view as well.

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